The present invention relates, in general, to amplifier circuits, and more particularly, to amplitude and phase correction for amplifiers.
Amplifiers and buffers in a receiver often use a differential input stage to generate differential output signals that ideally are equal in amplitude and separated in phase by 180 degrees. Amplitude equalization and a stable phase relationship are required by mixer circuits that receive a Radio Frequency (RF) modulated signal. The RF signal is downconverted to a lower Intermediate Frequency (IF) according to buffered differential signals received from a local oscillator. The incoming modulated signal is frequency shifted and the modulation is recovered in the IF signal.
Mismatches in the characteristics of devices used in the differential input stage can occur during the processing operation of the integrated circuit, which causes undesired amplitude differences and phase imbalance of the generated differential output signals. Further, a single-ended signal received as an input of the differential input stage has different delay paths in generating each of the differential output signals. The difference in the delay paths causes an undesired phase relationship between the differential output signals, especially at high frequencies of the single-ended input signal.
Accordingly, it would be advantageous to have a differential input stage that generates differential output signals equal in amplitude and separated in phase by 180 degrees. It would be a further advantage for the differential input stage to operate at high frequencies while maintaining the desired differential phase and amplitude balance.